A known seat reclining apparatus for a vehicle disclosed in JP2001-340154A (hereinafter referred to as Reference 1, see paragraphs 0010 to 0013, FIGS. 2 to 4) is attached to a seat cushion. The seat reclining apparatus includes a lower arm attached to a seat cushion, an upper arm attached to a seat back, first and second wedge members, a spring arranged between the first and second wedge members, and a drive shaft driving the first and second wedge members to rotate relative to the lower arm. The lower arm includes an internal gear and a first circumferential portion formed coaxially with the internal gear and having an outer circumferential surface. The outer circumferential surface of the first circumferential portion has a small diameter. The upper arm includes an external gear and a second circumferential portion having an inner circumferential surface. The inner circumferential surface of the second circumferential portion has a large diameter that is larger than the small diameter of the outer circumferential surface of the first circumferential portion. The number of teeth of the external gear of the upper arm is less than the number of teeth of the internal gear of the lower arm. The first and second wedge members are accommodated in a crescent-shaped accommodating space formed between the second circumferential portion and the first circumferential portion contacting the second circumferential portion. The wedge members frictionally engage with and disengage from the first and second circumferential portions. Further, the spring consistently biases the first and second wedge members in a direction engaging the first and second wedge members with the first and second circumferential portions.
In the seat reclining apparatus configured as above, when the drive shaft rotates, one of the first and second wedge members is moved against a biasing force of the spring and the other of the first and second wedge members is moved and pressed in the same direction of the movement of one of the first and second wedge members. Thus, the first and second wedge members are rotated relative to the lower arm to sequentially change an engagement position between the internal gear of the lower arm and the external gear of the upper gear accordingly. As a result, the upper arm is rotated relative to the lower arm depending on a difference between the teeth of the external gear and the teeth of the internal gear; therefore an angle of the upper arm relative to the lower arm is adjusted.
In addition, a seat reclining apparatus for a vehicle disclosed in JP2004-187759A (hereinafter referred to as Reference 2, see paragraphs 0017 to 0019, FIG. 4, and FIG. 9) has the approximately similar configuration to the configuration of the seat reclining apparatus described in Reference 1. The seat reclining apparatus described in Reference 2 is different from that of Reference 1 in that the first and second wedge members have finned portions, respectively. The finned portions are configured so as to be contactable with an axial end face of a cylinder portion that is formed on either one of the internal gear and the external gear and that supports therein the drive shaft to be rotatable. When a load is applied to either one of the internal gear and the external gear, the first and second wedge members may tilt relative to the cylindrical portion. At this time, the finned portions make contact with the axial end face of either one of the internal gear and the external gear to prevent the tilt movement of the first and second wedge members. As a result, the seat reclining apparatus smoothly operates without a variation of the engagement position between the external gear and the internal gear.
In References 1 and 2 described above, in the case where a tilt angle of the seat back is adjusted by the seat reclining apparatus and the seat back reclining apparatus is operated again in order to readjust the tilt angle of the seat back after a long period of time elapses following the previous adjustment of the tilt angle, i.e. after respective circumferential contact surfaces of the first and second wedge members are maintained in frictional contact with the inner circumferential surface of the second circumferential portion of the upper arm for a long period of time, a noise may occur only at an initial stage of the re-operation of the seat reclining apparatus. A reason of the occurrence of the noise is as follows.
When the respective circumferential contact surfaces of the first and second wedge members are pressed against the inner circumferential surface of the second circumferential portion of the upper arm under a high contact surface pressure, a lubricant such as grease applied to the circumferential contact surfaces is removed or released therefrom. At this time, even when the first and second wedge members are required to move after a long period of time while the circumferential contact surface is maintained without the lubricant, the first and second wedge members do not move until a certain degree of torque is applied to the first and second wedge members. This is because of a large static frictional force between the circumferential contact surfaces of the first and second wedge members and the inner circumferential surface of the second circumferential portion of the upper arm. When the torque to be applied to the first and second wedge members exceeds a predetermined value, the first and second wedge members suddenly start moving and therefore cause the noise between the circumferential contact surfaces of the first and second wedge members and the inner circumferential surface of the second circumferential portion.
A need thus exists for a seat reclining apparatus for a vehicle, which is not susceptible to the drawback mentioned above.